1. Field of the Invention
The present invention relates to a fuel hose that includes a resin barrier layer having low permeability to fuel in a middle in a radial direction or in a cross-section thereof and transports a fuel, for example, a filler hose of a resin-rubber composite for transporting a fuel to a fuel tank.
2. Description of the Related Art
In a filler hose adapted for transporting a fuel injected in a fuel inlet to a fuel tank in a motor vehicle, a typical rubber hose made of a blend of acrylonitrile-butadiene rubber and polyvinyl chloride (NBR/PVC blend, NBR+PVC) or the like has been conventionally used. Such rubber hose of NBR+PVC has a high vibration-absorbability, easiness of assembly, and a relatively excellent low permeability to fuel (gasoline).
However, such typical rubber hose cannot sufficiently meet to requirements for low permeability to fuel, which increase more and more recently.
As a countermeasure against that, developed and used is a filler hose that is a hose of a resin-rubber composite. The filler hose includes a resin layer that is laminated as an inner surface layer on an inner side of an outer rubber layer. The resin layer has an excellent low permeability (permeation resistance) to fuel, and defines a barrier layer.
However, the resin barrier layer is hard since resin is a material harder than rubber. So, in a filler hose including the resin barrier layer laminated on an inner side of the outer rubber layer to an axial end of the hose, when the filler hose is fitted on a mating pipe, sealing performance are insufficient due to poor contact between the mating pipe and the resin barrier layer that defines an inner surface of the hose.
And, since the resin barrier layer defining the inner surface of the filler hose is hard and exhibits a large deformation resistance during fitting of the filler hose on the mating pipe, a great force is required for fitting or slipping the filler hose on the mating pipe. This causes a problem that easiness of connection of the filler hose and the mating pipe is impaired.
For the purpose of solution of the problem, a filler hose as shown in FIG. 4 is disclosed in Patent Document 1 as below.
In the Figure, reference numeral 200 indicates a filler hose of a resin-rubber composite, reference numeral 202 indicates an outer rubber layer, and reference numeral 204 indicates a resin barrier layer that is laminated on an inner side of the outer rubber layer 202 as an inner surface layer.
In the filler hose 200, on an end portion thereof to be connected to a mating pipe 206 made of metal, the resin barrier layer 204 is not laminated, and an inner surface of the outer rubber layer 202 is exposed to be fitted on the mating pipe 206 elastically in direct contact relation.
And, in order to prevent a problem that a fuel flowing inside penetrates between the exposed inner surface of the outer rubber layer 202 and the mating pipe 206, and permeates outwardly through the end portion of the outer rubber layer 202 on which the resin barrier layer 204 is not laminated, in the filler hose 200, an annular grooved portion 208 is formed in an end portion of the resin barrier layer 204, a ring-shaped elastic sealing member 210 made of a material such as fluoro rubber (FKM) and having low permeability to fuel is attached therein. The filler hose 200 is fitted on the mating pipe 206 so as to elastically contact an inner surface of the elastic sealing member 210 with the mating pipe 206.
A typical filler hose, including that shown in FIG. 4, is connected to and fixed on the mating pipe 206 by a hose clamp 214 that has a threaded tightening mechanism.
Meanwhile, in FIG. 4, reference numeral 212 indicates a bulged portion (bulge portion) bulging annularly in a radially outward direction on a leading end portion of the mating pipe 206. The filler hose 200 is fixed on the mating pipe 206 with the hose clamp 214 tightening radially inwardly an outer peripheral surface of an end portion of the outer rubber layer 202 where the resin barrier layer 204 is not laminated.
FIG. 5 shows specifically structure of the hose clamp 214.
As shown in the Figure, the hose clamp 214 has a metal tightening band 230 in a form of a strip and a tightening mechanism 234.
The tightening band 230 includes one end portion 230A and the other end portion 230B. The one end portion 230A is formed with slit-like slots, slit-like thread grooves or slits 240 for receiving threads, circumferentially spaced apart at equal pitch. The tightening band 230 is rolled into a ring in such manner that the one end portion 230A with the thread grooves 240 overlaps an outer side of the other end portion 230B, and the screw-operated tightening mechanism 234 is fixed on the other end portion 230B.
The tightening mechanism 234 comprises a housing 236 fixed on the other end portion 230B, and an externally threaded screw 238 including a threaded stud that is rotatably received in the housing 236. Threads of the externally threaded screw 238 fit in and engage with the aforementioned slits 240.
In the case of the hose clamp 214, as the externally threaded screw 238 is rotated, the one end portion 230A is moved counterclockwise circumferentially (in FIG. 5) along the other end portion 230B, by screw feed mechanism, and the tightening band 230 is diametrically contracted to tighten and fix an end portion of the filler hose 200, specifically the outer rubber layer 202 as shown in FIG. 4 on the mating pipe 206.
In the filler hose 200 shown in FIG. 4, the resin barrier layer 204 is not laminated on an end portion of the filler hose 200. Therefore, a resistance of the resin barrier layer 204 is not greatly exerted when the filler hose 200 is fitted on the mating pipe 206, and thereby the filler hose 200 can be fitted thereon easily with a small force.
And, in the end portion of the filler hose 200, the resin barrier layer 204 is not formed, the inner surface of the outer rubber layer 202 having elasticity contacts directly with the mating pipe 206, and good sealing performance can be provided between the mating pipe 206 and a portion of the filler hose 200 fitted thereon.
By the way, the filler hose typically has a predetermined curved shape since the filler hose has to be arranged so as not to interfere with peripheral parts and components.
A typical rubber hose of such curved shape is produced in a following manner as disclosed also in Patent Document 2 as below. A rubber hose body of an elongate straight tubular shape is formed by extrusion, and the rubber hose is cut into a predetermined length to obtain a straight tubular rubber hose 216 (refer to FIG. 6) that is not vulcanized (or is semivulcanized). The straight tubular rubber hose 216 is fitted on a metal mandrel 218 that has a predetermined curved shape to be deformed into a curved shape. The curved tubular rubber hose 216 is vulcanized with being fitted on the mandrel 218 by heating for a predetermined period of time. When vulcanization is completed, the hose 220 of curved shape is removed from the mandrel 218, and now the hose 220 of curved shape as a finished product is obtained.
However, in the case of the filler hose 200 as shown in FIG. 4, such production method cannot be employed. In the case of the filler hose 200 as shown in FIG. 4, first of all, the outer rubber layer 202 is solely formed by injection molding, and then the resin barrier layer 204 is formed on the inner surface of the outer rubber layer 202 so as to follow a shape of the inner surface thereof.
For formation of the resin barrier layer 204 so as to follow the shape of the inner surface of the outer rubber layer 202, electrostatic coating means is suitably applied.
The electrostatic coating is applied in such manner that an injection nozzle is inserted into a filler hose, specifically into the outer rubber layer 202, and resin powder is sprayed from the injection nozzle onto an inner surface of the outer rubber layer 202, thereby the inner surface of the outer rubber layer 202 is electrostatically coated or painted with the resin powder.
In the electrostatic coating, a resin membrane is formed in such manner that negatively or positively charged resin powder (typically, negatively charged resin powder) is sprayed from the injection nozzle, and the resin powder flies to and is attached to the inner surface of the outer rubber layer 202 as counter electrode (positive electrode) by electrostatic field.
In steps of such an electrostatic coating, in order to form the resin barrier layer 204 with an intended thickness or wall-thickness, usually, more than one cycles of electrostatic coating are performed.
Specifically, after the resin powder is attached on the inner surface of the outer rubber layer 202, the resin powder is melted by heating and then cooled to form a resin membrane. Then, another resin powder is attached on the resin membrane by further spraying the another resin powder thereto by an electrostatic coating and the another resin powder is melted by heating and then cooled to form another resin membrane. In this manner, the cycle of electrostatic coating is repeated until the resin barrier layer 204 with an intended wall-thickness is formed.
In this case, overall production steps are as follows.
First, the outer rubber layer 202 is formed by injection molding. Then, the outer rubber layer 202 is dried, washed in pretreatment and dried again. Subsequently, resin powder is attached to an inner surface of the outer rubber layer 202 by electrostatic coating. The resin powder thereon is melted by heating and then cooled to form a resin membrane. After that, a second cycle of the electrostatic coating of resin powder, melting of resin powder by heating and cooling and caking of resin powder is performed to form another resin membrane on the resin membrane, and this cycle is repeated up to the required number of times to obtain the resin barrier layer 204 with the intended wall-thickness. After the resin barrier layer 204 is completed, a ring-shaped elastic sealing member 210 having fuel permeation resistance is inserted in a hose through an axial end of the outer rubber layer 202 to be placed in a predetermined position.
As stated above, a number of steps are required for producing the filler hose 200 as shown in FIG. 4, and therefore, production cost of the filler hose 200 is necessarily increased.
Accordingly, the inventors of the present invention devised and proposed in a prior patent application (for example, Japanese Patent Application No. 2006-89387) a filler hose of a resin-rubber composite, having a multilayer structure in which an inner rubber layer is further laminated on an inner side of a resin barrier layer as an inner surface layer.
FIG. 7 shows a specific example of the filler hose. The filler hose 246A of the multilayer structure is provided with low permeability (barrier properties) to a transported fluid by the resin barrier layer 244. Further, an inner rubber layer 242 that defines an inner surface of the filler hose 246A of the resin-rubber composite is elastically deformed when the filler hose 246A is fitted on a mating pipe 206. In this process, a force required for fitting the hose on the mating pipe can be decreased.
And, since the filler hose 246A is connected to the mating pipe 206 so as to elastically contact the inner rubber layer242 with the mating pipe 206, close contact is enhanced therebetween.
And, in the filler hose 246A of the multilayer structure, since the resin barrier layer 244 can be formed throughout to an axial end of the filler hose 246A, an expensive ring-shaped elastic sealing member 210 for providing permeation resistance to a transported fluid as shown in FIG. 4 can be omitted.
In addition, in the filler hose 246A of the multilayer structure, the resin barrier layer 244 can be formed throughout to the axial end of the filler hose 246A. This enables production of the hose 246A in the same production method as shown in FIG. 6.
Specifically, the inner rubber layer 242, the resin barrier layer 244 and the outer rubber layer 202 are laminated on one another by extrusion to form a rubber hose body of an elongate straight tubular shape, and the rubber hose body is cut into a straight tubular rubber hose. Now the straight tubular rubber hose that is unvulcanized or semivulcanized is obtained. Then, the extrudate, namely, the straight tubular rubber hose is fitted on a mandrel that has a predetermined curved shape to be deformed, the deformed tubular rubber hose with being fitted on the mandrel is completely vulcanized, and thereby the filler hose 246A with curved shape can be obtained.
This production method enables production of the fuller hose 246A at much lower cost than before.
By the way, a portion of the filler hose to fit on the mating pipe is designed to have an inner diameter smaller than an outer diameter of the mating pipe for securing connection by fitting an end portion of the filler hose on the mating pipe. Typically, the inner diameter of the end portion of the filler hose is smaller than the outer diameter of the mating pipe by approximately 1 mm to 2 mm. Namely, the end portion of the filler hose has a clamping allowance of approximately 0.5 mm to 1 mm.
A typical hose has an end portion of a single rubber layer. When the end portion of the typical hose is tightened by the hose clamp 214, a tightening force is exerted by the tightening band 230 uniformly throughout an entire circumference of an inner peripheral surface of the end portion of the typical hose, and the inner peripheral surface of the end portion of the typical hose is allowed to have favorable close contact with an outer peripheral surface of the mating pipe 206 throughout an entire circumference thereof. Thereby sufficient sealing performance are ensured between the end portion of the hose and the mating pipe 206.
However, the following problem is found in the filler hose 246A with a rubber-resin-rubber layered structure as shown in FIG. 7. In the filler hose 246A, a middle barrier layer 244 made of hard resin is formed throughout to an axial end of the filler hose 246A. When the filler hose 246A is fitted on the mating pipe 206 and an outer peripheral surface of an end portion of the filler hose 246A is tightened in a diametrically contracting direction by a hose clamp 214 similarly as in FIG. 4 to clamp (lock) the filler hose 246A onto the mating pipe 206 in connected relation, transmission of a clamping force by the hose clamp 214 is disturbed at the middle resin barrier layer 244, resulting that sealing performance cannot be achieved sufficiently as required between the end portion of the filler hose 246A and the mating pipe 26.
Then, the inventors of the present invention investigated the cause of the problem and found the following.
In the hose clamp 214 of a type shown in FIG. 5, when the externally threaded screw 238 is rotated, the one end portion 230A of the tightening band 230 is moved circumferentially along the other end portion 230B by screw feed mechanism, and the tightening band 230 is diametrically contracted.
The hose clamp 214 tightens the end portion of the hose as the tightening band 230 diametrically contracts, closely contacts an inner peripheral surface of the end portion of the hose with an outer peripheral surface of the mating pipe 206, and thereby provides a seal between the hose and the mating pipe 206.
However, in the case of the filler hose 246A of the resin-rubber composite including a hard resin barrier layer 244 in the middle in its thickness direction as shown in FIG. 7A, when the tightening band 230 is diametrically contracted to tighten the end portion of the filler hose 246A, an inner peripheral surface of the inner rubber layer 242 separates or rises partly and slightly radially outward from the mating pipe 206 as shown in a fragmentary enlarged view of FIG. 7B, resulting that sealing performance is insufficient in that region.
The cause is thought to be as follows. During diametrical contraction of the tightening band 230 for tightening the end portion of the filler hose 246A, the hard resin barrier layer 244 of the filler hose 246A in the middle in its thickness direction hinders the tightening force from being transmitted sufficiently to the inner rubber layer 242. And, during that time, the resin barrier layer 244 exhibits resistance to deformation in the diametrically contracting direction, a region of the end portion of the filler hose 246A tightened by the tightening band 230 is not diametrically contracted uniformly throughout an entire circumference thereof, a part near the end portion 230B of the tightening band 230 in fixed condition is deformed so as to rise slightly radially outward from the mating pipe. As a result, the sealing performance is partly impaired at the part near the end portion 230B of the tightening band 230 in fixed condition.
Namely, due to the resistance that is provided by the hard resin barrier layer 244 of the filler hose 246A in the middle in its thickness direction to deformation in the diametrically contracting direction, the end portion of the filler hose 246A, specifically the region of the filler hose 246A tightened by the tightening band 230 tends to be into a flat circular shape, and deformation and distortion are concentrated in the part near the end portion 230B of the tightening band 230 in fixed condition. This is thought to result in impaired sealing performance.
[Patent Document 1] JP-A, 2002-54779
[Patent Document 2] JP-A, 11-90993
Under the foregoing circumstances, it is an object of the present invention to provide a fuel hose such as filler hose including a hard resin barrier layer throughout an entire length of the fuel hose or throughout to an axial end of the fuel hose in the middle in a radial direction or thickness direction thereof where sufficient sealing performance is attained when clamped onto a mating pipe by a hose clamp.